The present invention is generally concerned with apparatus including sheet feeding and printing structures, and more particularly with a mailing machine including a base adapted to have mounted thereon a postage meter, and improved drive systems and control structures therefor.
This application is one of the following four, related, U.S. patent applications concurrently filed by A. Eckert, Jr. et. al. and assigned to the assignee of the present invention: Ser. No. 07/841,911 for Mailing Machine Including Sheet Feeding Speed Calibrating Means; Ser. No. 07/814,315 for Mailing Machine Including Printing Speed Calibrating Means; Ser. No. 07/841,915 for Mailing Machine Including Skewed Sheet Detection Means and Ser. No. 07/841,912 for Mailing Machine Including Short Sheet Length Detecting Means. In addition, this application is related to each of the following five U.S. patent applications filed Dec. 19, 1991 by A. Eckert, Jr., et. al. and assigned to the assignee of the present invention: Ser. No. 07/810,257, now U.S. Pat. No. 5,251,554, for Mailing Machine Including Shutter Bar Moving Means; Ser. No. 07/810,255 for Mailing Machine Including Sheet Feeding Control Means; Ser. No. 07/810,256 for Mailing Machine Including Shutter Bar Control System; Ser. No. 07/810,258 for Mailing Machine Including Printing Drum Acceleration And Constant Velocity Control System; and Ser. No. 07/810,597, now U.S. Pat. No. 5,268,836, for Mailing Machine Including Printing Drum Deceleration And Coasting Control System.
As shown in U.S. Pat. No. 4,774,446, for a Microprocessor Controlled D.C. Motor For controlling Printing Means, issued Sep. 27, 1988 to Salazar, et. al. and assigned to the assignee of the present invention, there is described a mailing machine which includes a base and a postage meter removably mounted thereon. The base includes sheet feeding structure for feeding a sheet in a downstream path of travel through the machine, and includes two sheet sensing structures located a known distance from one another along the path of travel. And, the postage meter includes a rotary printing drum for printing postage indicia on a sheet while feeding the sheet downstream in the path of travel therebeneath. The sensors successively sense the sheet in the path of travel and provide successive signals to a microprocessor to permit the time lapse between the signals to be used for calculating a count corresponding to the sheet feeding speed. Moreover, the base includes a d.c. motor for driving the postage printing drum, and an encoder coupled to the drum drive shaft for providing signals indicative of the position thereof to a counting circuit which, in turn, provides a count to the microprocessor indicative of the peripheral speed of the postage printing drum. And, the computer is programmed to successively sample the counts corresponding to the sheet feeding speed and the speed of the periphery of the drum to adjust the motor drive between sampling time instants and generate a motor drive signal for causing the motor to drive the drum at a velocity which matches the peripheral speed of the drum with the sheet feeding speed.
Thus it is know in the art to provide a closed loop, sampled data, feed back control system in a mailing machine base for continuously matching the peripheral speed of a postage printing drum to the feeding speed of a sheet.
As shown in U.S. Pat. No. 4,864,505 for a Postage Meter Drive System, issued Sep. 5, 1989 to Miller, et. al. and assigned to the assignee of the present invention, there is described a mailing machine base having a postage meter mounted thereon, wherein the base includes a first d.c. motor for driving the postage printing drum via a drum gear in the meter, a second d.c. motor for driving the structure for feeding a sheet through the machine, and a third, stepper, motor for driving a linkage system connected in bearing engagement with the postage meter shutter bar for moving the shutter bar out of and into locking engagement with the drum drive gear.
Thus it is known in the art to provide three separate motors for driving the sheet feeding, shutter bar moving and postage printing drum driving structures in a mailing machine base. And, it is known to provide a stepper motor for driving a linkage system to move the postage meter shutter bar into and out of locking engagement with the drum drive gear.
As shown in U.S. Pat. No. 4,787,311, for a Mailing Machine Envelope Transport System, issued Nov. 29, 1988 to Hans C. Mol and assigned to the assignee of the present invention. There is described a mailing machine base having a postage meter mounted thereon, wherein the time lapse between spaced sensors in the path of travel of a sheet is utilized by a microprocessor for calculating a sheet feeding speed, and wherein the speed of a stepper motor, connected for driving the postage printing drum under the control of the microprocessor, is adjusted to match the peripheral speed of the drum with the sheet feeding speed.
Thus it is known in the art to provide a microprocessor driven stepper motor in a mailing machine base for driving a postage printing drum at a peripheral speed which matches the speed of a sheet fed therebeneath.
As noted above, the structures utilized in the prior art for sheet feeding, shutter bar moving and postage printing drum driving purposes include the sophisticated feedback control system of the '446 patent, which continuously controls the motion of a postage printing drum to conform the same to a trapezoidal-shaped velocity versus time profile, having a constant velocity portion which results in the peripheral speed of the drum matching the speed of sheets fed through a mailing machine, and include the relatively inexpensive alternative of the '311 patent, which includes a stepper motor operated for matching the peripheral speed of the drum to the sheet feeding speed without regard to the acceleration and deceleration velocity versus time profile characteristics of the drum. Each of such systems has its drawbacks, for example, encoders are expensive, as are software solutions which take into consideration the technical specifications of the motors controlled thereby. And both of such expenses are major considerations in competitively pricing mailing machines for the marketplace. Further, stepper motors are noisy, as are linkage systems, which tend to suffer from wear and tear over time and become noisy. Moreover, the combination of a stepper motor and linkage system for driving a shutter bar tends to cause the moving shutter bar to be noisy. In addition to being irritable to customers, noise normally signals wear and tear and, since mailing machines must normally withstand the wear and tear of many thousands of operational cycles in the course of their expected useful life, maintenance problems are compounded by the use of noisy systems in mailing machines. And, such considerations are of major importance in generating and retaining a high level of customer satisfaction with the use of mailing machines. Accordingly:
an object of the invention is to provide an improved, low cost, low operational noise level, mailing machine base;
another object is to provide improved microprocessor controlled sheet feeding, shutter bar moving and postage printing drum driving structures in a mailing machine base;
another object is to provide a microprocessor controlled d.c. motor for accelerating sheet feeding rollers at a substantially constant rate to a substantially constant sheet feeding speed;
another object is to provide a microprocessor controlled shutter bar moving system in a mailing machine base;
another object is to provide a microprocessor controlled d.c. motor for timely accelerating a postage meter drum from rest, in its home position, to a substantially constant velocity, and then maintaining the velocity constant;
another object is to provide a microprocessor controlled d.c. motor for timely controlling deceleration of a postage printing drum from a substantially constant velocity to rest in its home position;
another object is to provide a method and apparatus for calibrating the sheet feeding speed of sheet feeding rollers to conform the speed to a predetermined speed;
another object is to provide a method and apparatus for calibrating the printing speed of a rotary printing drum to conform the printing speed to the speed of a sheet fed thereto;
another object is to provide a method and apparatus for detecting skewed sheets fed to a mailing machine base; and
another object is to provide a method and apparatus for detecting sheets of insufficient length fed to a mailing machine for printing postage indicia thereon.